Method and an equipment for producing rapid condensation hydrogen storage alloy powder

ABSTRACT

The present invention relates to a method and apparatus of manufacturing nickel-metal-hydride alloy powder material. The furnace charge of nickel-metal-hydride alloy is melted in vacuum or argon atmosphere in this invention. After melting, the molten alloy is gas atomized to fine spherical powder or centrifugal atomized to flaky shape. Then the powders are fed into a hydrogen heat treatment chamber for hydrogen heat treatment and pulverization. This invention integrates the melting, pulverizing and hydrogen treatment of nickel-metal hydride alloy powder into a whole step. It can charge and pulverize continuously and is suitable for the large-scale industrialized production of homogeneous composition and least segregation nickel-metal hydride alloy powder.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus formanufacturing nickel-metal-hydride alloy powder by rapid solidification.More particularly, the present invention relates to a method andapparatus for manufacturing the AB₅ series and AB₂ seriesnickel-metal-hydride alloy powder.

BACKGROUND OF THE INVENTION

It is well known that hydrogen is a clean and ideal energy source withhigh energy density. The industrialized production ofnickel-metal-hydride alloy powder is one of the most important tasks ofpersonnel specialized in the metallurgical industry. The industrializedproduction of the nickel-metal-hydride alloy involves the manufacturingtechnology of the nickel-metal-hydride alloy and the relevantfacilities.

The related prior art is as follows:

The chemical compositions of AB₅ type nickel-metal-hydride alloy in theprior art are almost the same, that is, they are obtained bymodifications of LaNi₅ nickel-metal-hydride alloy invented in Holland in1968. Said modification lies in that a low-price mixture of rare earth(Mm) is used as a hydrogen adsorption element instead of high-puritymetal La. Optionally, a small amount of Ti, Zr, Ca and Mg is added ashydrogen adsorption elements for further increasing the hydrogenadsorption capacity of the nickel-metal-hydride alloy; or a part of Niis replaced by Co, Mn, Al, or 1 to 2 kinds of M elements (M representsV, Cr, Fe, W, Mo, Nb, B, Si, Sn, Zn, N and so on) are added forimproving anti-corrosion, cycling life and related comprehensiveproperties of the nickel-metal-hydride alloy, so as to ensure theperformance characteristics of Ni—MH battery, such as high capacity,long life, high reliability, and to reduce the raw material cost.

AB₅ type nickel-metal-hydride alloy now has developed into an alloyalmost the same as the MmNiCoMnAl series alloy. The ratio of hydrogenadsorption elements to non-hydrogen adsorption elements in AB₅ typenickel-metal-hydride alloy is generally 1:5, which is properly adjustedby the manufacturers according to their own conditions, by increasing orreducing the contents of hydrogen adsorption elements. The atomic amountof non-hydrogen adsorption elements is generally 4.8-5.2. The contentsof various other elements are commonly: Ni 1.5-3.5, Co 1.5-3.5, Mn0.1-1, Al 0.05-0.5. A small amount of metal M can be added with acontent of about 0.02-0.2.

There are mainly two types of mixed rare earth metal Mm, that is theLanthanum-enriched type and Cerium-enriched type. The contents of themain rare earth elements of La, Ce, Nd, Pr vary according to differentplaces of origin of the raw materials. Generally, the total amount of Laand Ce is more than 70% so as to ensure the hydrogen adsorption capacityof the nickel-metal-hydride alloy.

In the state of the art, the manufacture of nickel-metal-hydride alloymostly emphasized the use of Ni—MH battery for negative electrode. Forimproving the comprehensive properties of the electrode, the alloycomposition is adjusted and the alloy structure is improved accordingly.However, the prior art rarely concern the industrial production methodof nickel-metal-hydride alloy. The production methods of AB₅ typenickel-metal-hydride alloy mentioned in the prior art can be summarizedas follows:

1. Vacuum arc melting, casting and mechanical pulverizing method:

Mixed rare earth metal with high purity and proper particle size areblended metallic raw materials according to the proportion of alloycomposition, and placed in a water cooling copper crucible, thenevacuated and filled with Argon for arc melting. The above mixture needsto be melted several times for obtaining a homogeneous ingot, and thenpulverized mechanically. Nickel-metal-hydride alloy is obtained by usingthis method in Japanese patent document nos. P3-289644, P4-52242 andP4-168240. The productivity of this method is low and can only be usedin research work.

2. Vacuum induction melting, water cooled mould casting and mechanicalcrushing, pulverizing method:

As stated in Japanese patent document no. P3-188234, liquid metal, afterbeing melted in a vacuum and optionally argon atmospheric inductionfurnace, is cooled quickly in plate water-cooled copper mould. A castingot having a column structure is obtained and then the mechanicalcrushing and pulverizing are used for powdering. The resulting mixture,under vacuum and optionally argon atmospheric protection, is heattreated at 900 to 1200° C. for structural homogenization. In thismethod, it is difficult to control the stable quality of the cast ingotin the production of ingots of less than 10μ micro-crystal structure byusing large capacity induction furnace.

3. Liquid metal single roller quick quenching and mechanicalpulverization method:

Japanese patent document no. P2-301531 teaches that 5-15 mm blocks ofAB₅, AB₂ and AB type metal-hydride alloy are made at first, then crushedcoarsely and placed in a quartz tube for re-melting into liquid metalwith high frequency induction heating under argon atmosphere. Then theresulting material is processed into strips by a high speed rotating(2,000 rpm) water cooled copper roller (φ300×400 mm), and fine powder isobtained by mechanical pulverization. Compared with other methods in theprior art, the quick quenching can improve the cooling speed, controlthe micro-structure of nickel-metal-hydride alloy, and increase thecharge and discharge cycling life of the alloy powder.

4. Gas atomization method.

Japanese patent document no. P3-226408 teaches that AB₅ type liquidnickel-metal-hydride alloy could be atomized by high speed inert gas formanufacturing non-balance state nickel-metal-hydride alloy powder. Thus,it is possible to increase the capacity, depress the self-discharge ofNi—MH battery and prolong the cycling life.

The Japanese patent No.P5-222474 discloses that the powder is obtainedby the atomization of liquid AB₅ type nickel-metal-hydride alloyMmNiCoMnAl+Zr under an Argon protection atmosphere. The cooling speedis >500° C./sec. An alloy with least segregation, micro-crystal andhomogeneous structure can be obtained under homogenizing heat treatmentat 600-900° C. for 2-5 hours. The corrosion-resistant property of thealloy can be improved and cycling life can be extended. Said method issuitable to be used for manufacturing a negative electrode of highcapacity with an initial capacity of 300 mAh/g and long cycling life(with a charge and discharge cycling life of >500 times) Ni—MH battery.Said method can also omit the mechanical crushing and pulverizationsteps of casting an ingot and simplify the production process ofnickel-metal-hydride alloy powder. However, it cannot satisfy the scaleof industrial production.

5. High temperature reductive diffusion from rare earth oxide method.

In Japanese patent document no. P3-170601, high-purity rare earth oxideLa₂O₃ (purity 99.99%), high-purity nickel powder (purity 99.9%) of5.0-8.8μ, and reductive of high-purity Ca (purity 99%) are mixedhomogeneously. The diffusion reaction is then proceeded in the reactioncontainer at 970° C. for 1.5-4 hours. LaNi₅ alloy powder is obtainedthrough cooling, water washing and filtering off the reaction productCaO, with a composition of La 31.4%, Ca 0.43-0.61%, O₂ 0.06-0.12%. Theinitial capacity of the alloy is 295-297 mah/g.

In Japanese patent document no. P3-281710, a mixed rare earth oxide(La₂O₃ 50.63/27.61, CeO₂ 2.81/50.1, Pr₆O₁₁/4.32, Sm₂O₃ 0.20/0.10), Nipowder, and CoMmCuAl metal oxide powder are blended homogeneouslyaccording to the chemical equivalent proportions of thenickel-metal-hydride alloy, with a small amount of Ca, Mg or Li beingadded. After mixing, MmNiCoMnAl alloy can be obtained by a hightemperature reductive diffusion method, wherein the reaction temperatureis 1,000-1,200° C., and the reaction time is 4-6 hours. Combining therare earth oxide reduction, alloying and pulverization into one step cansave the steps of mechanical crushing and pulverization of a cast ingot,improve the heat conductivity, electric conductivity, and reduce thedanger of pulverization by hydrogenation. But, the technology is complexand can not be used in continuous production and cannot satisfy therequirement of large-scale production.

Except the aforementioned manufacturing methods, the methods andequipment for further homogeneous treatment and hydrogen heat treatment,especially the facilities for hydrogen heat treatment, ofnickel-metal-hydride alloy powder are rarely reported. After studying,the applicants find that the further homogeneous treatment and hydrogenheat treatment of nickel-metal-hydride alloy powder can obtain amicro-crystal and homogeneous alloy structure with little segregation incomposition, increased thermo-resistance and extended charge anddischarge cycling life.

This invention is particularly developed for overcoming the shortcomingspresent in the existing method and equipment for manufacturing ofnickel-metal-hydride alloy powder.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method ofmanufacturing nickel-metal-hydride alloy powder. This method is simple,feasible, highly efficient and suitable for the large scale andcontinuous industrialized production of nickel-metal-hydride alloypowder.

Another object of the present invention is to provide facilities forvacuum and optionally argon atmospheric induction melting and highpressure inert gas atomization suitable for manufacturing thenickel-metal-hydride alloy powder described in this invention;

A further object of the present invention is to provide facilities forcentrifugal atomization and rapid solidification for manufacturingnickel-metal-hydride alloy micro-crystal powder.

Still another object of the present invention is to provide a spiraltype hydrogenating continuous heat treatment apparatus suitable formanufacturing the nickel-metal-hydride alloy powder described in thisinvention.

The manufacturing method described in this invention comprises the stepsof:

(a) pre-treating the raw materials to obtain an intermediate alloy toprevent the volatilization of the volatile component;

(b) melting the pretreated raw materials, the intermediate alloy thereofor a master alloy using a vacuum and optionally argon atmosphericinduction furnace to form a molten alloy;

(c) atomizing the molten alloy using a high-pressure inert gas orcentrifugal atomization to form an atomized alloy;

(d) passing the powder through a sieve;

(e) treating the powder with a hydrogen treatment to obtain the finalproduct.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the schematic structural drawing of the vacuum and optionallyargon atmospheric melting and high pressure inert gas atomizationfacilities described in the present invention.

FIG. 2 is the structural schematic drawing of the centrifugalatomization and rapid solidification facilities described in the presentinvention.

FIG. 3 shows the spiral type nickel-metal-hydride alloy powderhydrogenating continuous heat treatment facilities described in thepresent invention.

FIG. 4 shows the internal pressure curve of an AA-type battery describedin the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The numbers marked on the attached FIGS. 1-3 are defined as follows:

As shown in FIG. 1, the vacuum and optionally argon atmospheric meltingand high pressure inert gas atomization powdering facilities 20comprises vacuum chamber 1, induction furnace 2, intermediate ladle 3,middle pouring tube 15, high pressure inert gas atomizer 4, gasatomization chamber 5, cooling cone 6, fluidized bed 7, super-finepowder collector 8, conveying pipe 9, intermediate material tank 10,vibrating sieve 11, powder storage container 12, 13, vacuum chamber wall14, pouring port 16, discharging port 17, control valve 18 and ringshape nozzle 19 (18 and 19 are not shown in the drawing).

As shown in FIG. 2, the centrifugal powdering facilities 30 comprisevacuum chamber 21, charger 22, water cooling copper crucible 23,crucible pouring port 24, vacuum evacuating port 25, centrifugalrotating disk 26, collecting disk 27, scraper 28, and collector 29. Asshown in FIG. 3, the hydrogenating continuous heat treatment facilities40 comprise hydrogenation chamber 31, spiral vibrating pulverizer 32,heating coil for spiral conveying pipe 33, feeder 34, discharger 35,intermediate material storage container 36, vibrating sieve 37, materialstorage container 38, and hydrogen cylinder 39.

There are two kinds of methods to produce nickel-metal-hydride alloypowder described in the present invention, one is vacuum and optionallyargon atmospheric melting and high pressure inert gas atomization; theother is centrifugal atomization and rapid solidification; detaileddescriptions are as follows:

The manufacturing method of nickel-metal-hydride alloy powder by vacuumand optionally argon atmospheric melting and high pressure inert gasatomization described in the present invention includes:

A. pre-treatment of the raw materials and furnace charge:

(1) The main compositions, such as the elements of La, Ce, Nd, Pr etc.in the mixed rare earth metals (Mm) available in the market offered bydifferent manufacturers or under different brand numbers from amanufacture, are different. The compositions of Mm supplied from someproduction places and manufacturers in China are listed in Table 1.

TABLE 1 Places of Factory, Sm & other production Brand No. La Ce Nd Prelements A (1) 54.8 1.9 33.7 9.7 (2) 75.1 5.28 0.57 19.71 (3) 75 5.0<0.1 20.0 B (4) 41-51 3-5 35-41 9-11 Sm 0.5 Y < 0.5 (5) 26 47 18 9 C (6)57 16 18 9 (7) 85 2 13 (8) 99 D (9) 30.4 49.9 14.9 4.7 (10)  25-35 40-45 5-15 2-10 E (11)  28.1 49.97 15.37 4.7 Sm 0.12 F (12)  41-51 3-5 35-4120

In order to ensure the steady quality of MmNiCoMnAl seriesnickel-metal-hydride alloy produced in large scale, it is necessary tostabilize the quality of raw materials. The Mm put in use is premixedstrictly according to technical requirements, then melted using a vacuuminduction furnace to adjust the ratio of main compositions. Thepre-treated raw material of desired particle size is prepared and packedin vacuum to prevent oxidation.

(2) In order to control the effective addition amounts of the volatilealloy additives during vacuum melting of nickel-metal-hydride alloy, theintermediate alloys, for example, NiMg alloy, NiB alloy, BaAl alloy andso on, are prepared first.

(3) The preparation of MmNiCoMnAl master alloy.

B. The vacuum and optionally argon atmospheric melting and high pressureinert gas atomization

The pretreated furnace charge, i.e. said intermediate alloy ornickel-metal-hydride master alloy mentioned above in section A is meltedin a vacuum and optionally argon atmospheric induction furnace. Anatomized alloy is formed when the molten alloy is atomized byhigh-pressure inert gas or centrifugal atomization. The atomized alloyis cooled at a cooling speed in the range from 1,000 to 5,000° C./secondby a high-purity inert gas. The nickel-metal-hydride alloy powder with aspherical shaped micro-crystal structure can be obtained. The vacuum andoptionally argon atmospheric melting is carried out in an inductionelectric furnace, and the molten alloy is atomized by a high purityinert gas (99.999%) under a pressure in the range from 40 to 60atmospheres, and then is rapidly cooled and solidified to form aspherical shaped micro-crystal structure powder of the size from 120 to350 mesh.

The method of vacuum and optionally argon atmospheric melting and highpressure inert gas atomization for producing nickel-metal-hydride powdercan be carried out in the powdering facilities shown in FIG. 1 of thisinvention. The process of continuous charging and rapid pulverizing andcontinuous production can be fulfilled by using said facilities.

Said facilities can manufacture alloy powder under the protection of aninert gas atmosphere, such as Argon. The facilities for manufacturing anickel-metal-hydride alloy powder by vacuum and optionally argonatmospheric melting-atomization comprise:

(a) a vacuum chamber wall 14 defining the vacuum chamber 1;

(b) an induction electric furnace 2 disposed in the lower middle part ofthe vacuum chamber 1 and having a pouring port 16;

(c) an intermediate ladle 3 disposed under the pouring port 16;

(d) a middle pouring tube 15 disposed under the intermediate ladle 3;

(e) a high-pressure inert gas atomizer 4 disposed under the middlepouring tube 15;

(f) a gas atomization chamber 5 disposed under the high-pressure inertgas atomizer 4;

(g) a cooling cone 6 disposed at the lower part of the gas atomizationchamber 5;

(h) a fluidized bed 7 disposed at bottom of the gas atomization chamber5;

(i) a super-fine powder collector 8 disposed at the upper part of thegas atomization chamber 5;

(j) one end of a conveying pipe 9 connected to the side wall of thefluidized bed 7;

(k) an intermediate material tank 10 connected to the other end of theconveying pipe 9 opposite the fluidized bed 7;

(l) a discharging port 17 comprising the lower part of the intermediatematerial tank 10;

(m) a vibrating sieve 11 connected to the discharging port 17; and

(n) one or more powder storage containers 12, 13 connected to thevibrating sieve 11.

The pretreated charge is melted in vacuum induction furnace 2, and themolten alloy is poured into an intermediate ladle 3 after a temperatureadjusting step. By passing the molten alloy through a middle pouringtube 15 connected to the intermediate ladle 3, the molten alloy isintroduced into an inert gas atomizer 4 at a desired temperature andflow rate.

By passing the high-pressure inert gas having a pressure in the rangefrom 40 to 60 atmospheres into a ring-shaped nozzle through a controlvalve 18, liquid metal flow is atomized into from 120 to 350 mesh powderby the process of gas atomization. The cooling speed of said liquidalloy is normally in the range from 1,000 to 5,000° C./sec. A highlyhomogeneous, spherically shaped alloy powder with little segregation andmicro crystal structure can be obtained. The powder is cooled in anatomization chamber 5 and a cooling cone 6, and then further cooled on afluidized bed 7 using nitrogen gas, and sent by inert gas through aconveying pipe 9 into an intermediate storage tank 10, and dropped on acontinuous vibrating sieve 11 through a discharging port 17. The alloypowder is sieved into different particle sizes and is transferred intopowder storage container 12, 13 or other container, respectively.Finally, the nickel-metal-hydride alloy powder is vacuum packed.

A small amount of super-fine powder with a size of smaller than 10μ isremoved from the atomized alloy powder and collected in the super finepowder collector 8 that is connected to an upper part of the atomizationchamber 5. The inert gas used in the inert gas fluidized bed andconveying pipe 9 is the recycled inert gas that has been used in theprocess of high-pressure gas atomization.

The highly efficient, economical, stable and mass production ofnickel-metal-hydride alloy powder of high quality can be realized byusing the method and facilities of this invention.

Another method of this invention is the process of centrifugalatomization and rapid solidification. Details are as follows:

(a) Pretreatment of raw materials and furnace charge in this embodimentis the same as the process described in the above section A.

(b) Centrifugal atomization and rapid solidification manufacturing alloypowder.

The pretreated furnace charge, that is, the intermediate alloy from (a),or master alloy, is melted. The spheroidic shaped micro-crystal powderis obtained from the molten alloy by centrifugal atomization and rapidsolidification using a high speed rotating disk. Specifically, afterpretreatment, the furnace charge (master alloy) is melted in a vacuumargon arc furnace, the molten alloy is poured into a high speed rotatingdisk and atomized centrifugally into small liquid drops. After beingcooled on the collecting disk 27, the spheroidic shapednickel-metal-hydride alloy powder of 0.5-3 mm is obtained, having finemicro-crystal structure, with a grain size in the range of 0.05-5.0μ.The rotating speed of the high-speed centrifugal atomization rotatingdisk and the powder-collecting disk is in the range from 2,000 to 6,000rpm.

The process can be carried out in centrifugal atomization and rapidsolidification facilities 30 shown in FIG. 2 of this invention. Thefacilities 30 comprise; a vacuum chamber 21; two chargers 22 connectedto the vacuum chamber 21; a water-cooling copper crucible 23 disposed atthe center of the vacuum chamber 21 and having a pouring port; a vacuumevacuating port 25 disposed on a side wall of the vacuum chamber 21; acentrifugal rotating disk 26 disposed under the pouring port 24 of thecrucible 23; a collecting disk 27 adjacent and perpendicular to thecentrifugal rotating disk 26; a scraper 28 adjacent to the surface ofthe collecting disk 27 defining a fine clearance therebetween, and acollector 29 disposed under the collecting disk 27 for collecting powderscraped therefrom by the scraper 28. When running, two automaticchargers 22 of the same structure are opened and closed alternatively bymeans of a control valve and continuously charge the furnace charge orthe nickel-metal-hydride master alloy into the water-cooling coppercrucible 23 inside vacuum chamber 21. The pouring device comprises anautomatic tilting device for adjusting the tilting angle of the pouringport 24. The maximum vacuum at vacuum evacuating port 25 is 5×10⁻⁴ torr.

The centrifugal atomization system consists of a high speed centrifugalrotating disk 26 and a powder collecting disk 27 that is adjacent andperpendicular to centrifugal rotating disk 26. The rotating speeds ofthe two disks are both in the range from 2,000 to 6,000 rpm. The liquidmetal is poured into the high speed rotating disk 26 at a desired flowrate and is atomized into small liquid drops and thrown on collectingdisk 27 by centrifugal force. The drops solidified on the disk 27 enterinto collector 29 after being scraped off by scraper 28.

The powder obtained by high-speed rotating centrifugal atomization has aspheroidic shape with a radial size in the range from about 0.5 to 3.0mm and a thickness in the range from about 10 to 100μ. The powder has afine micro-crystal structure with a grain size in the range from 0.05 to5μ. The process of continuous charging, continuous melting andcontinuous powder making can be realized with the high-speed rotatingdisk centrifugal atomization facilities. Thus, it can not only reduceproduction cost, but can also increase production efficiency. The use ofthe water-cooling copper crucible can eliminate molten alloycontamination from crucible material and reduce non-metallic impurities.The introduction of argon, nitrogen or other inert gas into the furnacecannot only accelerate melting, reduce oxidation of molten metal, butcan also uniformly heat molten metal. It is advantageous to themanufacture of nickel-metal-hydride alloy powder of micro-crystalstructure with little impurities and segregation.

The powder manufactured by the two methods mentioned above can behydrogenated in the hydrogenating treatment facilities 40 of thisinvention.

The hydrogenating treatment facilities 40 of this invention comprise:

(a) a hydrogen heat treatment chamber 31;

(b) a feeding port 41 disposed or the top of chamber 31, a feeder 34connected to the feeding port 41 for feeding nickel-metal-hydride alloypowder therethrough into the chamber 31;

(c) a hydrogen charging port 42 on the side wall of the chamber 31, anda hydrogen gas cylinder 39 disposed outside the chamber for feedinghydrogen of 99.999% purity into the chamber 31 via the hydrogen chargingport 42;

(d) a spiral vibrating pulverizer 32 disposed at the bottom portioninside the chamber 31;

(e) a spiral conveying chute 43 disposed on the upper part of the innerwall of the chamber 31;

(f) a spiral conveying chute heating coil 33 disposed inside the spiralchute 43;

(g) a discharging port 44 disposed on a side wall of the chamber 31, andconnected to a discharger 35;

(h) an intermediate material storage container 36 connected to the lowerend of the discharger 35 opposite the chamber;

(i) a vibrating sieve 37 disposed under the intermediate materialstorage container 36; and

(j) one or more material storage containers 38 disposed under thevibrating sieve 37.

The continuous hydrogen treatment of nickel-metal-hydride alloy powderof this invention comprises the steps of:

(a) Charging with a hydrogen cylinder 39 99.999% pure hydrogen throughthe hydrogen charging port 42 into the hydrogen heat treatment chamber31 of the hydrogenating treatment facilities to produce a hydrogenatmosphere;

(b) Feeding the nickel-metal-hydride alloy powder from the feeder 34into the hydrogen heat treatment chamber 31;

(c) Crushing and pulverizing the fed powder by means of a spiralvibrating pulverizer 32 disposed at the bottom of the chamber;

(d) Passing the pulverized powder into a spiral conveying chute 43 of aspiral conveying chute heating coil 33 along a spiral line, therebyheating the pulverized powder;

(e) Passing the heated powder through a discharge tube, a discharge port44; and a discharger 35;

(f) Introducing the discharged powder into an intermediate materialstorage container 36;

(g) Passing the stored powder into a vibrating sieve 37, wherein thepowder is separated into powder of different meshes; and

(h) Storing the separated powder in one or more material storagecontainers according to the different meshes of the powder.

The period for heating of the crushed powder in the spiral conveyingchute is generally from 5 to 20 minutes with the temperature not higherthan 850° C. The hydrogen treatment process can be performed eitherunder normal pressure (760 mmHg) or at a pressure of 10 bar.

The spiral type hydrogen continuous heat treatment facilities of thisinvention can be used either for continuous homogeneous treatment andhydrogen heat treatment or be used with other production facilitiestogether in complete set and thus form a whole set of continuousproduction equipment and technology of powdering, hydrogen activationtreatment and sieving for the manufacture of nickel-metal-hydride alloypowder. The highly efficient, high quality, economical, stable andlarge-scale industrialized production of nickel-metal-hydride alloypowder material can be realized.

EXAMPLE 1

The powdering facilities for vacuum and optionally argon atmosphericmelting and high-pressure inert gas atomization shown in FIG. 1 andmethod for manufacturing nickel-metal-hydride alloy powder by vacuum andoptionally argon atmospheric melting and high-pressure inert gasatomization of this invention are used to produce AB₅nickel-metal-hydride alloy powder.

The process of treating the raw material and the furnace charge are thesame as that described above.

In order to control the amount of volatile alloy during vacuum melting,the intermediate alloys such as NiMg alloy, NiB alloy, BaAl and so onare prepared first.

In order to prevent the harmful elements and impurities fromcontaminating the nickel-metal-hydride alloy, the physical data of theraw material, such as chemical composition, surface quality, block sizeand so on are strictly inspected. The charge is added strictly accordingto technical requirements of casting ingot for controlling stablequality.

The pre-treated furnace charge is melted under vacuum, and thenoptionally in an argon atmosphere, in induction furnace 2, and liquidmetal is poured into an intermediate ladle 3 and middle pouring tube 15after a temperature control step. The molten alloy is introduced into ahigh-pressure inert gas atomizer 4 with ring shaped nozzle at a desiredtemperature and flow rate. The inert gas having a pressure in the rangeof 40-60 atmosphere is introduced through control valve, then moltenalloy is atomized to form a 120 to 350 mesh powder which is subsequentlycooled by gas atomization chamber 5 and cooling cone 6 and introducedinto a fluidized bed. In the fluidized bed 7, the powder is furthercooled by inert gas. The alloy powder is sent by inert gas into anintermediate tank 10 through a conveying pipe 9, then continuouslysieved by a vibrating sieve 11 for sieving into products of differentparticle sizes. The product is loaded into a storage container 12 andsealed in vacuum or inert gas.

The powder smaller than 10 μm formed during atomization is collected bya super-fine powder collector 8.

EXAMPLE 2

The facilities of high speed rotating disk centrifugal atomization andrapid solidification shown in FIG. 2 and the corresponding method ofthis invention are suitable for manufacturing AB₅, AB and AB₂ types ofmetal hydride alloy powder.

In this example, the process of pretreatment of the raw material andfurnace charge is the same as that mentioned above.

The pretreated raw material is charged through two automatic chargers 22of the same structure. During operation, the two chargers opened andclosed alternatively by means of control valves, so that the pretreatedraw material is added continuously into a water-cooling copper crucible23 inside a vacuum chamber 21 for performing melting. The molten liquidmetal in the copper crucible 23 is poured into a high-speed centrifugalatomization rotating disk 26 at a desired flow rate, and atomized intosmall liquid drops, then thrown onto a powder collecting disk 27 anddropped into a material storage container 29 after being scraped down bythe scraper 28. The rotating speed of centrifugal atomization disk 26and collecting disk 28 is in the range from 2,000 to 6,000 rpm. Thepowder manufactured has a spheroidic shape, and the thickness of thepowder is in the range from 10 to 100 μm, and its grain size is in therange from 0.5 to 5.0 μm.

EXAMPLE 3

As shown in FIG. 3, the hydrogen heat treatment chamber 31 provided bythis example of the invention is a cylindrical chamber, comprising:

(k) a hydrogen heat treatment chamber 31;

(l) a feeding port 41 disposed on the top of the chamber 31, a feeder 34connected to the feeding port 41 for feeding nickel-metal-hydride alloypowder therethrough into the chamber 31;

(m) a hydrogen charging port 42 disposed on the side wall of the chamber31, hydrogen gas cylinder 39 disposed outside the chamber for feedinghydrogen of 99.999% purity into the chamber 31 therethrough;

(n) a spiral vibrating pulverized 32 disposed at the bottom portioninside the chamber 31;

(o) a spiral conveying chute 43 disposed on the upper part of the innerwall of the chamber 31;

(p) a spiral conveying chute heating coil 33 disposed inside the spiralchute 43;

(q) a discharging port 44 disposed on a side wall of the chamber 31, andconnected to a discharger 35;

(r) an intermediate material storage container 36 connected to the lowerend of the discharger 35 opposite the chamber;

(s) a vibrating sieve 37 disposed under the intermediate materialstorage container 36; and

(t) one or more material storage containers 38 disposed under thevibrating sieve 37.

EXAMPLE 4

The grain size of nickel-metal-hydride alloy powder with high purity andfree of segregation manufactured by the method described in thisinvention is 0.05 to 5.0 μm, the powder size is in the range from 120 to350 mesh, and the capacity is 260 to 300 mAh/g. For examining theeletro-chemical properties of the powder, said nickel-metal-hydridealloy powder is mixed with a high-activity electric conductive additiveand bonding agent. The mixture is pasted on nickel foam to form a highcapacity negative electrode. The Ni—MH battery is obtained by matchingand separating said negative electrode with a pasting or sintering typepositive electrode. The properties of an AA type Ni—MH battery is shownin the following table.

4 hours 40 minutes 0.2 C capacity voltage 1.0 C capacity voltage Battery1 1360 mAh 1.244 V 1265 mAh 1.237 V Battery 2 1368 mAh 1.253 V 1283 mAh1.236 V Battery 3 1342 mAh 1.237 V 1247 mAh 1.235 V Charge current 0.4C, 3.5 hours; Discharge current 0.2 C, end voltage 1.0 V; and The chargeand discharge curves are shown in FIG. 4.

The method of this invention can integrate melting, powder pulverizingand hydrogenating of nickel-metal-hydride alloy into one whole torealize continuous production of nickel-metal-hydride powder. It issuitable for large-scale industrialized production. The cost isconsiderably reduced, while the quality and stability of the productcould be improved significantly. The charge and discharge properties ofbattery made by the powder of this invention are superior to that madeby the existing technique.

What is claimed is:
 1. A method of manufacturing a nickel-metal-hydride alloy powder by rapid solidification, comprising the steps of: (a) pre-treating a raw material, wherein the pre-treating comprises adjusting the composition of the raw material; (b) melting the pretreated raw material, an intermediate alloy thereof or a master alloy thereof of a desired particle size using vacuum or argon atmospheric induction to form a molten alloy; (c) atomizing the molten alloy using a high-pressure inert gas or centrifugal atomization to form an atomized alloy; (d) cooling and condensing the atomized alloy to form a nickel-metal-hydride alloy powder comprising micro-crystal particles of spherical or spheroidic shape; (e) passing the powder through a sieve; (f) treating the powder with a hydrogen treatment in a spiral hydrogen treatment apparatus; and (g) sealing the powder under vacuum.
 2. The method according to claim 1, wherein the melting is performed in a vacuum or argon atmospheric induction electric furnace.
 3. The method according to claim 2, wherein the maximum pressure at a vacuum excavating port of the vacuum or argon atmospheric induction electric furnace is 5×10⁻⁴ Torr.
 4. The method according to claim 1, further comprising the steps of: pouring the molten alloy into an intermediate ladle after a temperature control step; passing the molten alloy through a middle pouring tube connected to the intermediate ladle; and introducing the molten alloy into an inert gas atomizer at a desired temperature and flow rate to perform step (c).
 5. The method according to claim 4, wherein the high-pressure inert gas used in the inert gas atomizer is passed into a ring-shaped nozzle through a control valve.
 6. The method according to claim 5, wherein the high-pressure inert gas has a pressure in the range from 40 to 60 atmospheres.
 7. The method according to claim 4, wherein the nickel-metal-hydride alloy powder is from 120 to 350 mesh.
 8. The method according to claim 1, wherein the step (d) cooling of the atomized alloy is conducted at a cooling speed in the range from 1,000 to 5,000° C./second by a high-purity inert gas.
 9. The method according to claim 1, wherein in step (d), the powder is cooled in an atomization chamber and a cooling cone, and the powder is cooled on a fluidized bed using nitrogen gas.
 10. The method according to claim 1, further comprising the step of removing from the atomized alloy of step (c) micro-fine powder smaller than 10 μm in a powder collector.
 11. The method according to claim 1, wherein the step (a) of pre-treating a raw material comprises the step of adding rare-earth metals to the raw material.
 12. The method according to claim 1, further comprising the step of: continuously charging the pretreated raw material, an intermediate alloy thereof or a master alloy thereof of a desired particle size into a water-cooled copper crucible inside a vacuum chamber, for performing the vacuum or argon atmospheric melting using two chargers automatically and alternately opening and closing by controlling valves thereof.
 13. The method according to claim 1, further comprising the steps of: pouring the molten alloy from a pouring port of a pouring device into a high-speed centrifugal atomization rotating disk at a desired flow rate, the molten alloy being atomized into a nickel-metal-hydride alloy powder and thrown by centrifugal force therefrom; collecting the nickel-metal-hydride alloy powder thrown from the atomization rotating disk on a powder-collecting disk; scraping the nickel-metal-hydride alloy powder off the powder-collecting disk using a scraper; and collecting the nickel-metal-hydride alloy powder in a material storage container.
 14. The method according to claim 13, wherein the rotating speed of the high-speed centrifugal atomization rotating disk and the powder-collecting disk is in the range from 2,000 to 6,000 rpm.
 15. The method according to claim 13, wherein the pouring device comprises an automatic tilting device for adjusting the tilting angle of the pouring port.
 16. The method according to claim 13, wherein the nickel-metal-hydride alloy powder comprises flat spheroidic shaped particles having a thickness in the range from about 10 to 100 μm and a radial size in the range from about 0.5 to 3.0 mm.
 17. The method according to claim 1, wherein the step (f) of treating the powder with a hydrogen treatment comprises the steps of: charging with a hydrogen charger 99.999% pure hydrogen through a hydrogen charging port into a hydrogen heat treatment chamber of the hydrogen treatment apparatus to produce a hydrogen atmosphere; feeding the nickel-metal-hydride alloy powder into the hydrogen heat treatment chamber using a feeder; crushing the fed powder using a spiral vibrating crusher disposed at the bottom of the chamber; passing the crushed powder into a spiral conveying chute of a spiral conveying chute heating coil along a spiral line, thereby heating the crushed powder; passing the heated powder through a discharge tube, a discharge port, and a discharger; introducing the discharged powder into an intermediate material storage container; passing the stored powder into a vibrating sieve, wherein the powder is separated into different grades; and storing the separated powder in one or more material storage containers according to the different grades of the powder.
 18. The method according to claim 17, wherein the period for the heating of the crushed powder is from 5 to 20 minutes.
 19. The method according to claim 18, wherein the maximum temperature of the heating is 850° C.
 20. The method according to claim 19, wherein the powder is crushed using a spiral vibrating crusher at atmospheric pressure.
 21. The method according to claim 19, wherein the powder is crushed using a spiral vibrating crusher at a pressure of 10 bar.
 22. The method according to claim 1, wherein the high-pressure inert gas is nitrogen gas or argon gas having a purity of 99.999%.
 23. The method according to claim 1, further comprising the step of adding rare-earth metals to the raw material, the intermediate alloy thereof or the master alloy thereof during step (a). 